This invention relates to a radial ply pneumatic truck tire. More particularly it teaches an improved tread profile for a low aspect ratio tire commonly referred to in the tire art as a Super Single tire.
Historically in the mid 1960's, The Goodyear Tire & Rubber Company introduced a bias tire construction in which one such tire could replace two conventional truck tires on two axle semi-trailers. During 1965, the Bias Super Single tires were produced in Wolverhampton, England. The wear rate and overall durability of these tires were poor and therefore the cost benefits of a single tire versus two conventional tires in a dual fitment were not fully realized.
In the mid seventies Michelin introduced the first All Steel Radial Super Single tire. Goodyear around 1976 also introduced such a radial tire called the G165.
In Europe the tri-axle full trailers were introduced in Germany and tri-axle semi-trailers in France. These changes reduced the drive axle loads from typically 13 to 11 metric tons. The tri-axle gross vehicle weight (GVW) load was limited to 22 metric tons. This greatly increased to usage of Super Single tires. In the mid 1980's the Continental Europe GVW of tractor/semi-trailers and truck/full trailers was increased from 38 to 40 metric tons. This change in GVWmade two-axle semi-trailer vehicle in dual tire fitments uncompetitive in view of payload and thus forced truck line haul accounts to exchange old two-axle units with tri-axle ones, further increasing the demand for Super Single tires. The tri-axle trailer GVW was increased to 24 metric tons and the tire load was increased from 4,125 kg to 4,500 kg.
These increases in load limits have naturally required improved durability of the Super Single type tire. The truck owners and operators see their inventories of six Super Single tires and rims versus twelve conventional tires and rims per each tri-axle trailer as a signification cost advantage. The mounting of Super Single tire and rim assemblies is less labor intensive. The resultant weight savings when using Super Single tires means more payload can be carried and these wide tires have superior rolling resistance yielding fuel cost savings.
All these benefits are achievable if the tires can be designed with sufficient treadwear and durability. Truck tires are more than any other tire valued based on their load capacity and their miles of useful life. The present invention has significantly improved the useful life of this type of tire while also providing sufficient load capacity.
In the past the tread has been contoured employing a rather simple single or dual radius of curvature originating internal of the tire. This configuration can yield a footprint shape that resembles a butterfly on a wide low aspect ratio tire such as a Super Single. The present invention corrects this inherently poor wearing footprint shape and yields a substantially rectangular footprint that has no butterfly appearance.